1. Field
The present invention relates generally to sensor systems, and more particularly, to a method and apparatus for tire pressure monitoring.
2. Background
There are two fundamental goals that a tire pressure monitoring system (TPMS) should fulfill for the management system of a vehicle—accuracy and speed of measurements of tire pressure.
Most tire pressure losses result from slow leaks that have a deleterious effect on vehicle handling, fuel consumption, and tire life. When the pressure loss is slight, however, there is generally no immediate danger of catastrophic tire failure. Therefore, although it is important to measure tire pressure with a high degree of accuracy to be able to detect slow air pressure leaks, the timing of these accurate measurements is not critical. In contrast, if a tire loses pressure rapidly, it is important that a driver be warned as soon as possible. In these cases, it is not critical that the rapid tire pressure loss be measured with a high degree of accuracy—an error of measurement of up to 10% of the original pressure is probably acceptable. Thus, in certain circumstances, even an inaccurate but timely pressure measurement will increase the overall system functionality at detecting significant events, thus improving the safety of the system.
Typically, the tire pressure monitoring device is a battery-powered, self-contained sensor device that is mounted inside a wheel. The device transmits measured pressure to a receiver inside the vehicle via a wireless signal. Because the pressure sensor in these devices requires a significant power to operate, many existing systems compromise performance for battery life. For example, to reduce the power utilized by the sensors, the frequency of measurements is decreased when the vehicle is not in motion. Typically a roll switch, which is a switch that is operated by a rolling motion, or an accelerometer is used to detect whether the vehicle is in motion. The inclusion of these types of motion detection devices to provide this functionality increases the cost while reduces reliability of the system and, even with this functionality, conventional systems only measure pressure about every 30 seconds, meaning that a rapid tire pressure loss could still result in an accident before the driver is warned.
It is desirable to be able to provide a TPMS system that has reduced power consumption while improving reliability as compared to current TPMS systems.